Inbound calls to our server are seeing 503s returned just sort of randomly. Could this be related to box load? Is there anything that should go to the logfiles in this case? Are there any settings we could tweak to reduce the issue?
If there is load shedding, you would see task processor queue overflow messages.
I half remember there is another problem, possibly with refreshing registrations, that can cause occasional failures.
Generally, in all cases, if you set an appropriate logging level, you should see some reason given.